Patterning process is one of many processes used in manufacturing electronic devices, including integrated circuit (IC) devices. It is a process used to form features on a substrate, on which the devices are formed. One of the patterning processes used is photo-lithography. In this process, a layer of photoresist is deposited on a substrate. Thereafter, a mask having with an aperture arranged in a desired pattern is disposed is positioned between the substrate and a light source. The radiation from the light source is then directed toward the substrate, and the pattern of the aperture in the mask is imaged on the photoresist. Thereafter, the photoresist is exposed to a developer solution, such as tetramethyl ammonium hydroxide. As the radiation exposure causes the photoresist to become soluble to the developer solution, the portion of the photoresist exposed to the radiation is dissolved and removed from the substrate. Meanwhile, another portion not exposed to the radiation may remain insoluble and remain on the substrate as the resist structures. The remaining resist structures, which may correspond to the aperture pattern of the mask, may be baked and further hardened. These resist structures may be used as a mask for subsequent, for example, etching process, and the features corresponding to the resist structures may form on the substrate.
With increased demand for smaller devices with more complex circuitry, the feature size requirement has become more stringent. Unfortunately, limitations in the scaling of the photolithography systems can no longer meet the device scaling requirements. For example, it has been found that the conventional photolithography may result in resist structures with excessive line edge roughness (LER) or line width roughness (LWR), instead of smooth well defined resist structures. If present, LER or LWR from the resist structures is transferred to the substrate below during the etching process, and these defects may be transferred onto the substrate. Such defects may result in device degradation usually in transistor or parametric stability. Depending on the design, short, medium or long range roughness will have detrimental impact on the device.
Accordingly, a new process that limits or reduces the LER and LWR in photolithographic process is needed.